Calibration of sensors

ABSTRACT

A plurality of seismic sensors calibration method ( 100 ) includes: an assembling so that sensors are coupled with each sensor positioned with its axis of sensitivity in a different spatial direction calibration system step ( 105 ), a rotating sensors step ( 110 ), a measuring sensors output signals step ( 115 ), a sensor output signal processing step ( 120 ) and a storing calibration coefficient(s) step ( 125 ).

This application claims benefit of application No. 60/125,076 filed Mar. 17, 1999.

BACKGROUND OF THE INVENTION

The present disclosure relates generally to a method of calibrating a plurality of sensors, and in particular to a three-axis sensor.

In deploying sensors, calibration coefficients are used to correct the sensors for variations or errors in gain, offset, non-linearity, misalignment of the proof masses, cross-axis coupling, temperature, or other environmental factors and to provide more accurate seismic data. Some limitations of current calibration methods include no automatic calibration, no conversion of data to internationally accepted scientific units, no permanent storage of the data, and no universal usage by any and all seismic software.

The present invention is directed to overcoming or at least minimizing some of the limitations of the existing methods of calibrating sensors.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a method of calibrating a plurality of seismic sensors, each sensor having an axis of sensitivity, is provided that includes: coupling the sensors with each sensor positioned with its axis of sensitivity in a different spatial direction; rotating the sensors; measuring one or more output signals from the sensors; processing the output signals from the sensors; and storing one or more calibration coefficients.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of a method for calibrating a plurality of sensors.

FIG. 2A is a schematic view of an embodiment of a calibration system for use in the method of FIG. 1.

FIG. 2B is a schematic view of an embodiment of the sensors of the calibration system of FIG. 2A.

FIG. 2C is a schematic view of an embodiment of the controller of the calibration system of FIG. 2A.

FIG. 3 is a schematic view of rotating the sensors and measuring output from the sensors of the calibration method of FIG. 1.

FIG. 4 is a schematic view of a preferred embodiment for processing output from the sensors and storing calibration coefficients to the sensors of the calibration method of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Several embodiments of a method for calibrating a plurality of sensors are provided. The sensors are calibrated to correct for variations or errors in gain, offset, non-linearity, misalignment of the proof masses, cross-axis coupling, temperature, or other environmental factors and to provide more accurate seismic data. In a preferred embodiment, a system for calibration includes a plurality of sensors and a controller. The sensors are calibrated by rotating the sensors, obtaining data from the sensors, calculating the calibration coefficients for the sensors, and storing the calibration coefficients. The controller gathers the sensor data and calculates the calibration coefficients. The controller preferably includes a computer data acquisition system and a computer software program.

Referring initially to FIG. 1, a preferred embodiment of a method 100 for calibrating a plurality of seismic sensors includes: (1) assembling a calibration system in step 105; (2) rotating the sensors in step 110; (3) measuring output from the sensors in step 115; (4) processing output from the sensors in step 120; and (5) storing one or more calibration coefficients in step 125. In a preferred embodiment, the steps 105, 110, 115, and 120 of the method 100 preferably incorporate the methods disclosed in the Institute of Electrical and Electronic Engineers Specification IEEE 337-1972 for the IEEE Standard Specification Format Guide and Test Procedure for Linear, Single-Axis, Pendulous, Analog Torque Balance Acclerometer, attached as Appendix A.

Referring to FIG. 2A, in step 105, a calibration system 200 preferably includes a plurality of sensors 205 and a controller 210. In a preferred embodiment, the calibration system 200 includes a first sensor 205 a, a second sensor 205 b, and a third sensor 205 c. The sensors 205 are preferably coupled to the controller 210 by one or more communication interfaces 215. In a preferred embodiment, the calibration system 200 includes a first communication interface 215 a, a second communication interface 215 b, and a third communication interface 215 c. The first sensor 205 a is preferably coupled to the controller 210 by the first communication interface 215 a. The second sensor 205 b is preferably coupled to the controller 210 by the second communication interface 215 b. The third sensor 205 c is preferably coupled to the controller 210 by the third communication interface 215 c. The communication interfaces 215 may, for example, be parallel. In a preferred embodiment, the communication interfaces 215 are serial in order to optimally provide reduced wiring complexity.

The first sensor 205 a preferably includes an axis of sensitivity 220. The axis of sensitivity 220 is preferably approximately parallel to the x-axis. The first sensor 205 a is preferably coupled to the second sensor 205 b and the third sensor 205 c to maintain the axis of sensitivity 220 parallel to the x-axis. The second sensor 205 b preferably includes an axis of sensitivity 225. The axis of sensitivity 225 is preferably approximately parallel to the y-axis. The second sensor 205 b is preferably coupled to the first sensor 205 a and the third sensor 205 c to maintain the axis of sensitivity 225 parallel to the y-axis. The third sensor 205 c preferably includes an axis of sensitivity 230. The axis of sensitivity 230 is preferably approximately parallel to the z-axis. The third sensor 205 c is preferably coupled to the first sensor 205 a and the second sensor 205 b to maintain the axis of sensitivity 230 parallel to the z-axis. More generally, the axis of sensitivity 220 is in a first direction, the axis of sensitivity 225 is in a second direction, and the axis of sensitivity 230 is in a third direction and the directions need not be orthogonal to one another when the sensors 205 are coupled.

Referring to FIG. 2B, each of the sensors 205 preferably include a seismic sensor 235 and an application specific integrated circuit (“ASIC”) 240. The design and operation of the seismic sensor 235 and the ASIC 240 are preferably substantially as disclosed in the following co-pending U.S. patent application Ser. No. 09/936,640, filed on Sep. 12, 2001, Ser. No. 09/936,634, filed on Sep. 12, 2001, and Ser. No. 08/935,093, filed on Sep. 25, 1997, the contents of which are incorporated herein by reference. The ASIC 240 preferably further includes a local non-volatile memory 245. The local non-volatile memory 245 may be, for example, PROM, EPROM, EEPROM, flash memory or traditional NVM. In a preferred embodiment, the local non-volatile memory 245 is EEPROM in order to optimally provide permanent reprogrammable data storage.

Referring to FIG. 2C, the controller 210 preferably includes a computer data acquisition system 250 and a computer software program 255. The controller 210 may, for example, be a mechanical fixture and a PC. In a preferred embodiment, the controller 210 is a motor driven rotation stage in order to optimally provide better repeatability and automation in the method 100. The computer data acquisition system 250 may, for example, be a voltmeter. In a preferred embodiment, the computer data acquisition system 250 is PC-based using counter A/D, D/A and digital I/O boards in order to optimally provide automation. The computer software program 255 may be, for example, C code. In a preferred embodiment the computer software program 255 is a commercial package utilizing graphical user interfaces in order to optimally provide ease of programming, debugging and usage.

Referring to FIG. 3, in step 110, the sensors 205 are preferably rotated around the x-axis, the y-axis and the z-axis. The sensors 205 may, for example, be rotated at angle increments ranging from about 30 to 90 degrees. In a preferred embodiment, the sensors 205 are rotated at angle increments ranging from about 45 to 90 degrees in order to optimally provide the minimum required accuracy.

In step 115, the sensors 205 preferably transmit one or more output signals 305 to the computer data acquisition system 250 of the controller 210 as the corresponding sensors 205 are rotated. In a preferred embodiment, a first output signal 305 a, a second output signal 305 b, and a third output signal 305 c are transmitted from the first sensor 205 a, the second sensor 205 b, and the third sensor 205 c, respectively. The computer data acquisition system 250 of the controller 210 preferably stores the output signals 305 from the corresponding sensors 205. The output signals 305 are preferably measured at each angle the corresponding sensors 205 are rotated about in step 110.

Referring to FIG. 4, in step 120, the output signals 305 from the corresponding sensors 205 are preferably processed by the computer software program 255 of the controller 210. The computer software program 255 of the controller 210 preferably calculates one or more calibration coefficients 405 from the outputs 305 of the sensors 205. In a preferred embodiment, a first calibration coefficient 405 a, a second calibration coefficient 405 b, and a third calibration coefficient 405 c are generated for the first sensor 205 a, the second sensor 205 b, and the third sensor 205 c, respectively, to the controller 210.

In step 125, the calibration coefficients 405 are stored. The calibration coefficients may be stored, for example, in the local non-volatile memory 245 or an external database. In a preferred embodiment, the calibration coefficients are stored in the local non-volatile memory 245 of the corresponding sensor 205 in order to optimally provide storage of data in the calibrated unit. The first calibration coefficient 405 a, the second calibration coefficient 405 b, and the third calibration coefficient 405 c are preferably downloaded to the first sensor 205 a, the second sensor 205 b, and the third sensor 205 c, respectively.

A method of calibrating a plurality of seismic sensors, with each sensor having an axis of sensitivity, has been described that includes coupling the sensors, with each sensor positioned with its axis of sensitivity in a different spatial direction, rotating the sensors, measuring the output signals from the sensors, processing the output signals from the sensors, and storing one or more calibration coefficients. In a preferred embodiment, the sensors comprise micro-machined accelerometers. In a preferred embodiment, coupling the sensors with each sensor positioned with its axis of sensitivity in a different spatial direction includes coupling the sensors with the axes of sensitivity in the x-direction, the y-direction, and the z-direction. In a preferred embodiment, rotating the sensors includes rotating the sensors about the x-axis, the y-axis and the z-axis. In a preferred embodiment, measuring output from the sensors includes measuring the output signals from the sensors at one or more angles of rotation. In a preferred embodiment, processing output from the sensors includes calculating one or more calibration coefficients from the measured output signals of the sensors. In a preferred embodiment, each sensor further includes a corresponding ASIC having a local non-volatile memory. In a preferred embodiment, storing one or more calibration coefficients to the sensors includes storing the corresponding calibration coefficients to the corresponding local non-volatile memories in the corresponding ASIC. In a preferred embodiment, storing one or more calibration coefficients to the sensors includes storing the corresponding calibration coefficients to an external database. In a preferred embodiment, coupling, rotating, measuring, and processing are provided in accordance with the Institute of Electrical and Electronic Engineers Specification IEEE 337-1972 for the IEEE Standard Specification Format Guide and Test Procedure for Linear, Single-Axis, Pendulous, Analog Torque Balance Acclerometer.

Although illustrative embodiments of the invention have been shown and described, a wide range of modification, changes and substitution is contemplated in the foregoing disclosure. In some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention. 

What is claimed is:
 1. A method of calibrating a plurality of seismic sensors, each sensor having an axis of sensitivity, comprising: positioning the sensors with each sensor positioned with its axis of sensitivity in a different spatial direction; rotating the sensors; measuring one or more output signals from the sensors; processing the one or more output signals from the sensors; and storing one or more calibration coefficients.
 2. The method of claim 1, wherein the sensors comprise micro-machined accelerometers.
 3. The method of claim 1, wherein coupling the sensors with each sensor positioned with its axis of sensitivity in a different spatial direction comprises, coupling the sensors with the axes of sensitivity in: a first direction; a second direction; and a third direction.
 4. The method of claim 1, wherein rotating the sensors comprises, rotating the sensors about the x-axis, the y-axis and the z-axis.
 5. The method of claim 1, wherein measuring one or more output signals from the sensors comprises, measuring the output signals from the sensors at one or more angles of rotation.
 6. The method of claim 1, wherein processing the output signals from the sensors comprise, calculating one or more calibration coefficients from the measured output signals of the sensors.
 7. The method of claim 1, wherein each sensor further includes a corresponding ASIC having a local non-volatile memory; and wherein storing one or more calibration coefficients includes storing the corresponding calibration coefficients to the corresponding local non-volatile memories.
 8. The method of claim 1, wherein storing one or more calibration coefficients includes storing the corresponding calibration coefficients to a database external to the sensors.
 9. The method of claim 1, wherein coupling, rotating, measuring, and processing are provided in accordance with the Institute of Electrical and Electronic Engineers Specification IEEE 337-1972 for the IEEE Standard Specification Format Guide and Test Procedure for Linear, Single-Axis, Pendulous, Analog Torque Balance Accelerometer. 